FIG. 10 is a partly sectional view of a general recording head. The recording head has: a base plate 46, piezoelectric vibrating members 42 vibratably contained and mounted in a containing space 53 formed in the base plate 46, and a passage unit 47 fixed to an under surface of the base plate 46.
The passage unit 47 has: a nozzle plate 50 having openings such as nozzles 40, a thin vibrating plate 43 which can deform elastically, and a passage forming plate 49 sealingly fixed between the nozzle plate 50 and the vibrating plate 43. In the passage forming plate 49, pressure chambers 41 respectively communicating with the nozzles 40, an ink saving chamber 48 for temporarily saving ink supplied into the pressure chambers 41, and ink supplying passages 51 respectively connecting the pressure chambers 41 and the ink saving chamber 48 are formed. On the other hand, the base plate 46 has an ink way 55 connecting to the ink saving chamber 48 through an ink supplying hole 52. Thus, new ink is supplied into the ink saving chamber 48 through the ink supplying hole 52.
The arrangement of the ink supplying hole 52, the ink saving chamber 48 and the pressure chambers 41 is explained with reference to FIG. 11. As shown in FIG. 11, the ink saving chamber 48 has a flat trapezoidal shape. The ink supplying hole 52 is connected to a substantially middle portion of the ink saving chamber 48. The pressure chambers 41 and the ink supplying passages 51 are arranged in parallel with each other in one side of the ink saving chamber 48. Each of the pressure chambers 41 and each of the ink supplying passages 51 are perpendicular to the longitudinal direction of the ink saving chamber 48. The pressure chambers 41 are respectively communicated to the nozzles 40.
Each of the piezoelectric vibrating members 42 is fixed to a supporting plate 54 fixed in the containing space 53 of the base plate 46 in such a manner that the piezoelectric member 42 can vibrate in the containing space 53. A lower end of the piezoelectric vibrating member 42 adheres to an island portion 43a of the vibrating plate 43 of a passage unit 47.
The recording head operates as below. At first, electric power is supplied to a piezoelectric vibrating member 42. Then, as shown in FIGS. 12a and 12b, the piezoelectric vibrating member 42 contracts with respect to a normal original state thereof, a pressure chamber 41 expands with respect to a normal original state thereof, and the pressure therein is reduced. Thus, a meniscus 46 of ink in a nozzle 40 is dented toward the pressure chamber 41, and ink in an ink saving chamber 48 is supplied into the pressure chamber 41 through an ink supplying passage 51.
When electric charges are discharged from the piezoelectric vibrating member 42 after a predetermined time, the piezoelectric vibrating member 42 returns to the original state thereof, as shown in FIG. 12c. Then, the pressure chamber 41 contracts and the pressure therein is increased.
Thus, the ink in the pressure chamber 41 is pressed to jet from the nozzle 40 as ink drops, which form images or characters on the recording paper.
In the above recording head, the ink 44 in the nozzles 40 may dry up and clog the nozzles 40 while the recording head remains stopped after a printing operation. Then, the nozzles are sealed by a capping unit except while the recording head is in the printing operation. However, a solvent of the ink 44 in the nozzles 40 may gradually evaporate to increase a viscosity of the ink 44 if the nozzles are sealed for a long time. In that case, it may be difficult to start a printing operation immediately. In addition, there may be some troubles, including that the quality of printed images may deteriorate.
During the printing operation, the nozzles 40 frequently jetting inkdrops 45 are scarcely clogged with the ink 44 because new ink 44 is supplied thereinto in succession. However, even during the printing operation, the nozzles 40 rarely jetting inkdrops 45 (for example, the nozzles arranged at an upper end portion or a lower end portion) are liable to be clogged with the ink 44 because the ink 44 in such nozzles 40 is liable to dry to increase the viscosity thereof.
To solve the above problems, a "flushing operation" or a "cleaning operation" is carried out by forcibly discharging the clogging ink 44 from the nozzles 40 in no relation to the printing operation, to recover the ability of the nozzles 45 to jet inkdrops. The above flushing or cleaning operation may be carried out when power supply starts to be given to the recording apparatus or when a first printing signal is inputted to the recording apparatus, as a preparatory step before the printing operation.
In the flushing operation, a driving signal in no relation to the printing data is supplied to the piezoelectric vibrating members 42 to jet the clogging ink 44 having a relatively increased viscosity from the nozzles 40. The cleaning operation is carried out when the ability of the nozzles to jet inkdrops is not sufficiently recovered by the flushing operation. In the cleaning operation, a suction pump applies a negative pressure to the nozzles 40 to forcibly absorb the clogging ink 44 having a relatively increased viscosity from the nozzles 40.
The degree of the increasing viscosity of the ink 44 in the nozzles 40, i.e., the degree of clogging the nozzles 40, becomes worse depending on the length of the capping time for which the recording head remains sealed by the capping unit or on the length of the total printing time until, the recording head is sealed by the capping unit.
Therefore, as shown in FIG. 13, whether the flushing operation or the cleaning operation should be carried out is determined by the combination of the capping time and the total printing time. The flushing operation is carried out when the capping time or the total printing time is relatively short (see a flushing area in FIG. 13). The cleaning operation is carried out when the capping time or the total printing time is relatively long (see a cleaning area in FIG. 13).
In the above apparatus, when ink in the pressure chambers 41 is consumed for a flushing, cleaning or printing operation, new ink is supplied from the ink supplying hole 52 into the pressure chambers 41 through the ink saving chamber 48. Then, the new ink supplied from the ink supplying hole 52 flows easily into the pressure chambers 41 disposed near to the ink supplying hole 52. However, on the contrary, it is difficult for the new ink supplied from the ink supplying hole 52 to flow into the pressure chambers 41 disposed far from the ink supplying hole 52. Thus, there may be a difference in viscosity of the ink in the different portions of the ink saving chamber 48. That is, the viscosity of the ink at a portion near to the ink supplying hole 52 may be different from the viscosity of the ink at a portion far from the ink supplying hole 52.
For example, as shown in FIG. 11, the viscosity of the ink in the ink saving chamber 48 may be highest to lowest in the order of D area, C area, B area and A area. In that case, volumes of ink jetted from the nozzles 40 far from the ink supplying hole 52 in the flushing operations may be small when the same driving signal is used for all of the pressure chambers 41. Thus, ink having an increased viscosity might remain in the pressure chambers 41 far from the ink supplying hole 52. That is, the ability of the nozzles 40 far away from the ink supplying hole 52 to jet ink might not be recovered sufficiently. In that case, there may be such a difference in the ability to jet ink due to the positions of the nozzles 40 so that the quality of printing may deteriorate.
In addition, when a flushing operation is carried out for a pressure chamber 41 in which ink having an increased viscosity remains, as shown in FIG. 14, a meniscus 46 of the ink may become unstable and dented deeply and obliquely to take an air bubble in the nozzle 40. Thus, a cleaning operation has to be carried out to remove the ink having the increased viscosity from the pressure chambers 41 far from the ink supplying hole 52, even when the ability to jet ink of the nozzles 40 near to the ink supplying hole 52 can be recovered by flushing operations. That is, a range of conditions wherein the ability of the nozzles 40 to jet ink can be recovered by only the flushing operations (which range is called a flushing area) is small.
In this case, a relatively larger volume of ink may be necessary to recover the ability of the nozzles 40 to jet ink. That is, the volume of ink capable of being used for the printing operation may be small, and the volume of the waste ink may be large.